Bone connector with pivotable joint

ABSTRACT

System, including methods, apparatus, and kits, for connecting bones and/or bone portions using a bone connector with a pivotable joint.

CROSS-REFERENCES TO PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/115,529, filed May 25, 2011, now U.S. Pat. No. 8,617,227.

U.S. patent application Ser. No. 13/115,529, in turn, is a continuationof U.S. patent application Ser. No. 11/431,740, filed May 9, 2006, nowU.S. Pat. No. 7,951,198, which, in turn, claims the benefit under 35U.S.C. §119(e) of the following U.S. provisional patent applications:Ser. No. 60/679,710, filed May 10, 2005; and Ser. No. 60/701,891, filedJul. 21, 2005.

Each of these priority applications is incorporated herein by referencein its entirety for all purposes.

INTRODUCTION

The skeletal portion of the human wrist, shown in FIG. 1, includes sevencarpal bones 20. The carpal bones are disposed in transverse proximal 22and distal 24 rows composed of three bones in the proximal row and fourbones in the distal row. These rows provide a transition between the twobones of the forearm (radius 26 and ulna 28) and the five metacarpals 30of the hand. The proximal row includes a scaphoid bone 32 and a lunatebone 34, among others. These bones articulate with one another (througha scapholunate joint 36), and also articulate proximally with radius 26(through a radiocarpal joint), and distally with distal row 24 of thecarpal bones.

Trauma to the wrist can produce scapholunate instability by injuring aligament, the scapholunate interosseous ligament (SLIL) 38, thatconnects the scaphoid and lunate bones. The SLIL normally restricts thesize of the scapholunate interval (the spacing) between the scaphoid andlunate bones and permits some limited relative rotation (about twentydegrees) of these bones about a nonfixed transverse axis extendingthrough these bones. Injury to the SLIL can lead to arthriticdegeneration of the radiocarpal joint and loss of wrist movement.

Chronic scapholunate instability may be treated with a screw, termed aHerbert screw 40. The Herbert screw extends across the scapholunatejoint and threads into both the scaphoid and lunate bones using spacedthreads of the screw. The Herbert screw may fix the scaphoid and lunatebones in position until engagement of the Herbert screw's thread withbone loosens enough over time to permit relative pivotal movement of thescaphoid and lunate bones about the screw's long axis. The Herbert screwthus restricts separation (i.e., relative translational motion) of thescaphoid and lunate bones both before and after pivotal movement ofthese bones is permitted by this screw.

The Herbert screw may have a number of disadvantages. For example, theHerbert screw may not permit bone movement for approximately six weeksafter installation, a time period sufficient to result in formation ofscar tissue and thus long term loss of wrist function. In addition, whenthe Herbert screw loosens its grip on bone, joint movement generally isrestricted substantially to a pivotal motion about a single axis definedby this screw. The scapholunate joint thus cannot achieve its fullanatomical range of articulation, and may be even more limited if theHerbert screw is installed at an unsuitable angle.

A number of other approaches also have been employed, alone or incombination, to treat scapholunate instability. These approaches mayinclude percutaneous pinning, direct repair of the SLIL, dorsalcapsulodesis, brunelli tenodesis, and SLIL reconstruction. However, eachof these approaches may be unsatisfactory for various reasons.

SUMMARY

The present teachings provide a system, including methods, apparatus,and, kits, for connecting bones and/or bone portions using a boneconnector with a pivotable joint.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a dorsal view of the bones of the right wrist with a Herbertscrew installed in and extending between the scaphoid and lunate bones.

FIG. 2 is a schematic, partially sectional view of an exemplary systemfor connecting bone members using a bone connector with a pivotablejoint, in accordance with aspects of the present teachings.

FIG. 3 is a partially sectional view of another exemplary system forconnecting bone members using a bone connector with a pivotable joint,with the bone connector configured as a bone screw and connectingscaphoid and lunate bones, in accordance with aspects of the presentteachings.

FIG. 4 is a side elevation view of the bone screw of FIG. 3 in theabsence of the scaphoid and lunate bones.

FIG. 5 is an exploded view of the bone screw of FIG. 3, taken as in FIG.4.

FIG. 6 is a sectional view of the bone screw of FIG. 3, taken generallyalong line 6-6 of FIG. 4.

FIG. 7 is an end view of a trailing screw element of the bone screw ofFIGS. 3-5, taken generally along line 7-7 of FIG. 5.

FIG. 8 is an end view of a leading screw element of the bone screw ofFIGS. 3-5, taken generally along line 8-8 of FIG. 5.

FIG. 9 is an exploded view of another exemplary bone screw with apivotable joint, in accordance with aspects of the present teachings.

FIG. 10 is a side elevation view of the bone screw of FIG. 9 in anassembled configuration.

FIG. 11 is a partially sectional view of the bone screw of FIG. 9, takengenerally along line 11-11 of FIG. 9.

FIG. 12 is a sectional view of still another exemplary bone screw with apivotable joint, in accordance with aspects of the present teachings.

FIG. 13 is a fragmentary sectional view of yet another exemplary bonescrew with a pivotable joint, in accordance with aspects of the presentteachings.

FIG. 14 is a side elevation view of an exemplary bone connector with apivotable joint and a pair of retention mechanisms that may be actuatedselectively after the bone connector is positioned in bone, inaccordance with aspects of the present teachings.

FIG. 15 is a sectional view of the bone connector of FIG. 14, takengenerally along line 15-15 of FIG. 14.

FIG. 16 is a side elevation view of an exemplary driver for installationof jointed bone connectors, in accordance with aspects of the presentteachings.

FIG. 17 is a fragmentary isometric view of the driver of FIG. 16,particularly showing a hexagonal tip region of the driver, takengenerally at “17” in FIG. 16.

FIG. 18 is a fragmentary isometric view of another exemplary driver forinstallation of jointed bone connectors, particularly showing a steppedhexagonal tip region of the driver, in accordance with aspects of thepresent teachings.

FIG. 19 is a schematic representation of an exemplary bone screw havinga cylindrical joint.

DETAILED DESCRIPTION

The present teachings provide a system, including methods, apparatus,and kits, for connecting bones and/or bone portions using a boneconnector with a pivotable joint (“a jointed bone connector”). Theconnector may include a pair of anchor elements. The anchor elements maybe configured to be inserted into bone in an ordered fashion, such as aleading anchor element configured to enter bone before a trailing anchorelement of the pair. In addition, each anchor element may have aretention structure that engages bone to secure the anchor element inbone. The anchor elements may be connected directly or indirectly to oneanother by a pivotable joint, such that separation of the anchorelements is restricted whether or not the anchor elements are engagedwith bone (i.e., the anchor elements are retained proximate one anotherin the absence of bone). The pivotable joint may be configured to permitrelative pivotal motion of the anchor elements about at least twononparallel axes. For example, the pivotable joint may permit relativepivotal motion (1) about the long axis of the connector so that theanchor elements can be twisted relative to another, and (2) about one ormore transverse axes of the connector so that the connector can be bentto place the anchor elements out of alignment. Accordingly, the shape ofthe connector may be flexible to accommodate, for example, (1) imperfectalignment of the connector with an anatomical axis of pivotalarticulation, and/or (2) a nonfixed anatomical axis of pivotalarticulation.

FIG. 2 shows an exemplary system 60 for connecting at least two bonemembers 62, 64 using a bone connector 66 with a pivotable joint 68. Bonemembers 62, 64 may be distinct bones or may be broken or cut fragmentsof the same bone.

Connector 66 may include at least a pair of anchor elements 70, 72. Theconnector may have a polarity provided by the anchor elements forinsertion into bone (or may be configured to be inserted in either axialorientation). For example, trailing anchor element 70 may be configuredto follow leading anchor element 72 into a hole 73 in proximal bonemember 62 during installation of the connector. Each anchor element mayhave a body 74, 76 and one or more retention structures 78, 80 thatengage bone to secure the anchor element in bone. The retentionstructures may, for example, extend laterally from the body and/or maybe created by the body, such as through deformation of the body in situ(see Example 5). Accordingly, the act of placing each anchor elementinto bone may provide securing engagement of each retention structurewith bone (such as when the connector is threaded into and/or pushedforcefully into bone), and/or at least one retention structure may bepart of a retention mechanism that can be actuated selectively afterplacement of a corresponding anchor element into bone. Furthermore, eachanchor element may have a driver engagement structure 82, 84 that allowsthe anchor elements to be driven into bone collectively and/orindependently by a suitable driver(s).

The anchor elements may be connected to one another directly orindirectly via pivotable joint 68. The pivotable joint may permit anysuitable relative pivotal motion of the anchor elements (and thus theirengaged bone members), such as a twisting motion, indicated at 86, abouta long axis 88 of the connector (and/or of an anchor element), and/or abending motion, indicated at 90, about a transverse axis 92 (or acontinuous range of transverse axes) defined by the joint.

FIG. 3 shows an exemplary system 110 for connecting bone members, suchas a scaphoid bone 112 and a lunate bone 114, using a connectorconfigured as a bone screw 116 with a pivotable joint 118, such as aball-and-socket joint. Bone screw 116 may include pivotably coupledscrews elements 120, 122 each having an external thread 124, 126 forengagement with bone. The bone screw may be installed, for example, byforming a hole 128 in scaphoid bone 112, and placing the leading screwelement into lunate bone 114 from the hole as trailing screw element 120is advanced into the hole.

Further aspects of the present teachings are described in the followingsections including (I) overview of jointed bone connectors and anchorelements, (II) retention structures, (III) pivotable joints, (IV) driverengagement structures, (V) connector compositions, (VI) fabrication ofjointed bone connectors, (VII) installation of jointed bone connectors,(VIII) kits, and (IX) examples.

I. OVERVIEW OF JOINTED BONE CONNECTORS AND ANCHOR ELEMENTS

A jointed bone connector of the present teachings may include two ormore components that are movable relative to one another and that haveany suitable structure. The components may include two or more discreteanchor elements that can engage bone to resist removal of each anchorelement. Each anchor element may be unitary (one piece) or may be formedof two or more pieces, such as two or more pieces that are affixed toone another. The jointed bone connector also may include one or moreother discrete components, such as one or more discrete spacercomponents disposed between the anchor elements and/or one or more endcomponents flanking the anchor elements adjacent one or both opposingends of the connector.

The anchor elements may have any suitable size and shape. The anchorelements may be about the same length (the characteristic dimensionmeasured parallel to the central axis) or different lengths. Forexample, the proximal (trailing) anchor element may be shorter or longerthan the distal (leading) anchor element. The anchor elements may haveabout the same diameter or different diameters. For example, theproximal anchor element may be wider (of greater diameter) than thedistal anchor element (e.g., to ensure engagement with bone throughwhich a narrower distal anchor element has traveled). The diameter ofeach anchor element may be generally constant or may vary along thelength of the anchor element. For example, the distal (and/or proximal)anchor element may taper distally, proximally, or both. Furthermore, theproximal and/or distal anchor element may have a distal tapered nose(threaded or nonthreaded) that enters bone first.

The jointed bone connector may include a spacer region. The spacerregion may have any suitable position(s) in the bone connector and/orwithin an anchor element relative to a retention mechanism of the anchorelement. For example, the spacer region may be disposed between athreaded region and a joint protuberance (and/or joint cavity) of ananchor element. The spacer region may be unitary with an associatedthreaded region (or other retention structure) of an anchor element ormay be formed by a distinct component joined fixedly (e.g., welded,bonded, or threadably coupled) or connected movably (e.g., coupled by amovable joint) to the threaded region (or other retention structure).The spacer region(s) may have any suitable length relative to thethreaded region (or other retention structure) of an anchor element,including shorter, longer, or about the same length as the threadedregion (or retention structure). Furthermore, the spacer region may haveany suitable diameter or width relative to the threaded region (orretention structure) and/or protuberance, including a lesser (orgreater) diameter or about the same diameter as that of the protuberanceand/or the minor diameter of the threaded region. The spacer region may,for example, provide a nonthreaded region (and/or a non-anchoringportion of an anchor element(s)) to be disposed at the interface betweenbone members in which the jointed bone connector is installed and/or mayhelp define a range of bending motion of the pivotable joint (seeSection III).

The connector may define any suitable size and shape of cavity for anysuitable purpose. The cavity may extend the entire length of the jointedbone connector, such that the connector is cannulated, or may, forexample, terminate before or after the cavity reaches the leading anchorelement and before it reaches the leading end of the jointed boneconnector. The cavity may have a constant or varying cross-sectionalgeometry, which may be constant or vary within or compared betweenanchor elements. In some examples, the cavity may define a driverengagement structure in both anchor elements, so that a driver mayextend through the leading anchor element and into the trailing anchorelement, for concurrent engagement and rotation of both anchor elements.In some examples, the cavity may be a recess that is restricted to anactuation element disposed in the proximal anchor element (see Example5). In some examples, the cavity may narrow (or end) as it extendsdistally in the leading anchor element, to provide a shoulder for a tipof the driver to bear against, to facilitate driving the connector intobone.

II. RETENTION STRUCTURES

Each anchor element may have any suitable retention mechanism. Theanchor element may include a retention mechanism that is actuated byplacement into bone and/or after placement into bone. The anchorelements of a jointed bone connector may have the same type of retentionmechanism (e.g., each having an external thread) or may have differenttypes of retention mechanisms (e.g., one having an external thread andanother having a nonthreaded engagement with bone).

A retention mechanism that is actuated by placement into bone may bedefined by an anchor element that has a cross-sectional dimension (suchas diameter) that is larger than the diameter of a hole into which theanchor element is placed. The anchor element thus may be disposed in afriction fit with bone (and/or may cut into bone) as it is placed intothe bone. In some examples, the cross-sectional dimension may be definedin part by one or more projections that extend laterally from the bodyof the anchor element. Exemplary projections may include an externalthread, one or more barbs, one or more circumferential ridges, one ormore hooks, and/or the like. The projections may be biased (e.g., angledtoward the trailing end of the anchor element), to facilitate insertionand to restrict removal. Alternatively, or in addition, the anchorelement may have a cross-sectional dimension that increases toward anend (such as a trailing end) of the anchor element (e.g., a flared(e.g., frustoconical) anchor element). Anchor elements that engage boneand resist removal as they are placed into bone may be driven into bonerotationally (e.g., threaded into bone) and/or translationally (e.g.,hammered into bone).

A retention mechanism that can be actuated in situ after placement of ananchor element into bone may be provided by expansion/deformation of theanchor element at a selected time after placement. Theexpansion/deformation may be any change in the structure of the anchorelement that increases a cross-sectional dimension of the anchor elementat one or more (or all) positions along the placement axis (e.g., thelong axis) of the anchor element. Further aspects of retentionmechanisms actuated selectively in situ are described in Example 5.

The jointed bone connector may be configured as a bone screw having oneor more anchor elements (“screw elements”) with an external thread. Theexternal thread may have any suitable thread structure. Each screwelement may include a single thread (e.g., a continuous rib and/orfurrow) or a plurality of threads. The plurality of threads may bedisposed in discrete axial regions of the screw element (e.g., spacedproximal and distal threaded regions on the screw element) and/or mayshare the same axial region (e.g., to produce a multi-threadedconfiguration). The thread (or threaded region) of each screw elementmay extend over any suitable portion of the screw element's length,including at least substantially the entire length or less than abouthalf the length, among others. The screw elements may have a thread ofthe same pitch or of different pitch. For example, the trailing screwelement may have a thread with a lesser (or greater) pitch than a threadof the leading screw element, to facilitate compression (or distraction)of associated bone members during installation of a jointed bone screw.In addition, the pitch within each screw element may be constant or mayvary, for example, decreasing (or increasing) toward the proximal end ofthe screw element. The thread may have any other suitable features. Forexample, the thread (and thus the corresponding screw element) may havea constant or varying major and/or minor diameter within a screw elementand/or between the screw elements.

In some embodiments of jointed bone screws, the screw elements, andparticularly the leading screw element, may be configured to beself-drilling and/or self-tapping as the bone screw is advanced intobone. For example, a leading end region of the leading screw element mayinclude a cutting structure(s) to drill bone, and/or a threaded regionof either or both screw elements may include a tap region (such as oneor more axial flutes and/or thread notches, among others) with a cuttingedge(s) to tap bone.

III. PIVOTABLE JOINTS

The anchor elements of a jointed bone connector may be connected by anysuitable joint. The joint may be a movable joint between the anchorelements, operating by relative sliding motion (pivotal and/ortranslational) of apposed joint constituents. The joint may operate torestrict complete separation of the anchor elements in the absence ofbone, while permitting relative pivotal and/or translational motion ofthe anchor elements. The joint may be a single connection between theanchor elements or a composite connection formed collectively by two ormore distinct movable joints.

The joint may be formed by slidable contact between the anchor elements.For example, the joint may be formed by a protuberance (e.g., a head) ofone anchor element received in a cavity defined by the other anchorelement. The protuberance may be provided by the trailing or leadinganchor element. The protuberance may be sized and/or shaped to bereceived and retained in the cavity. For example, the protuberance mayhave a characteristic dimension (such as width or diameter) that isgreater than the mouth of the cavity, such that the protuberance, afterbeing received in the cavity, resists withdrawal through the mouth.However, in some embodiments, the characteristic dimension may be closeenough to the size of the mouth that the protuberance can be forced intothe cavity through the mouth. The protuberance and the cavity may havegenerally complementary shapes or different shapes. In some examples,the protuberance and/or the cavity may be semispherical (that is, beingat least somewhat spherical in shape, to create a ball-and-socketjoint), cylindrical (such as a hinge joint), conical, and/or the like.The protuberance and cavity may correspond relatively closely in size,and/or the cavity may be somewhat larger in an axial and/or transversedirection, to permit, for example, axial and/or side-to-side (lateral)motion, respectively, of the protuberance within the cavity (e.g., seeExample 4).

The joint may permit any suitable relative motion. The joint may permitaxial translational motion and/or lateral translational motion, or maysubstantially restrict either or both of these motions. The joint alsoor alternatively may permit pivotal motion about the long axis and/orabout one or more transverse axes of the jointed bone connector. Thepivotal motion about the long axis may be unrestricted (allowing a fullturn) or restricted to less than a full rotation of the anchor elements.The pivotal motion about the transverse axes may be determined by thestructure of the pivotable joint and/or joint constituents, for example,allowing an angular range of motion, about a selected transverse axis,of at least about five degrees and/or no more than about 10, 20, 40, or90 degrees, among others.

IV. DRIVER ENGAGEMENT STRUCTURES

The jointed bone connector may have one or more structures forengagement with a driver, to facilitate driving the connector into bone.For example, only one of the anchor elements may have a driverengagement structure (see, e.g., Example 5), or each anchor element ofthe connector may have a driver engagement structure (see, e.g.,Examples 1-3). The driver engagement structures of the connector mayhave the same cross-sectional size and shape (see, e.g., Examples 2 and3) or may have different cross-sectional sizes or shapes (see, e.g.,Example 1). Accordingly, the driver engagement structures may be engagedconcurrently with the same driver, such as to rotate the anchor elementstogether, or at least one driver engagement structure may be engagedselectively, such as for selective rotation of an anchor element (e.g.,to adjust the spacing between bone members to a greater or lessspacing).

The driver engagement structure may be defined by a cavity (or cavities)or a projection(s). Exemplary cavities (i.e., through-holes, blindholes, and/or recesses) may have any suitable cross-sectional shape foruse with a rotational driver, such as polygonal, cruciform, rosette,slotted, circular (with a set of two or more laterally disposedcavities), etc. In some examples, a circular cross-sectional shape maybe suitable for use with a translational driver. Exemplary projectionsmay provide an external engagement surface, such as a hexagonal head,for engagement with a driver having a complementary socket.

Further aspects of driver engagement structures and exemplary driversare described elsewhere in the present teachings, such as in Example 6of Section IX.

V. CONNECTOR COMPOSITIONS

The connectors may be formed of any suitable biocompatible and/orbioresorbable material(s). Exemplary biocompatible materials include (1)metals (for example, titanium or titanium alloys; alloys with cobalt andchromium (cobalt-chrome); stainless steel; etc.); (2) plastics (forexample, ultra-high molecular weight polyethylene (UHMWPE),polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE),polyetheretherketone (PEEK), and/or PMMA/polyhydroxyethylmethacrylate(PHEMA)); (3) ceramics (for example, alumina, beryllia, calciumphosphate, and/or zirconia, among others); (4) composites; (5)bioresorbable (bioabsorbable) materials or polymers (for example,polymers of α-hydroxy carboxylic acids (e.g., polylactic acid (such asPLLA, PDLLA, and/or PDLA), polyglycolic acid, lactide/glycolidecopolymers, etc.), polydioxanones, polycaprolactones, polytrimethylenecarbonate, polyethylene oxide, poly-β-hydroxybutyrate,poly-β-hydroxypropionate, poly-δ-valerolactone, poly(hydroxyalkanoate)sof the PHB-PHV class, other bioresorbable polyesters, and/or naturalpolymers (such as collagen or other polypeptides, polysaccharides (e.g.,starch, cellulose, and/or chitosan), any copolymers thereof, etc.); (6)bone tissue (e.g., bone powder and/or bone fragments); and/or the like.In some examples, these materials may form the body of an anchor elementand/or a coating thereon. The anchor elements of a connector may beformed of the same material(s) or different materials. Exemplaryconfigurations with different materials may include a connector formedof metal with trailing anchor element formed of a titanium alloy and aleading anchor element formed of cobalt-chrome (or vice versa), or aconnector with a trailing anchor element formed of metal and a leadinganchor element formed of a bioresorbable material or of plastic (or viceversa), among others.

VI. FABRICATION OF JOINTED BONE CONNECTORS

The jointed bone connectors of the present teachings may be fabricatedby any suitable process(es). For example, the anchor elements of eachjointed bone connector may be formed separately and then connected toone another. Alternatively, the anchor elements may be formed at leastpartially after they have been connected.

Each anchor element may be formed by any suitable process(es). Exemplaryprocesses include molding, machining, casting, forming, crimping,milling, and/or the like. Threads or other retention structure on theanchor elements may be formed at the same time as and/or after formationof other portions of the anchor elements.

The anchor elements may be connected by any suitable process. Exemplaryprocesses include press-fitting a protuberance of one anchor element ina cavity of another anchor element, to form a pivotable joint. Thecavity may have a mouth that is narrower than the width of theprotuberance, so that the protuberance, once it is forced past themouth, remains trapped in the cavity. Other exemplary processes includedisposing a protuberance in a cavity having a lip, and then crimping orotherwise deforming the lip so that the protuberance is retained in thecavity. Additional exemplary processes include placing a protuberance ofa first anchor element in a cavity of a second anchor element, and thenattaching a cap or other retainer to the second anchor element over theprojection, such as by welding, bonding, with an adhesive, etc.

VII. INSTALLATION OF JOINTED BONE CONNECTORS

The jointed bone connectors of the present teachings may be installed byany suitable methods. Exemplary steps that may be performed are listedbelow. These steps may be performed in any suitable order, in anysuitable combination, and any suitable number of times.

At least two bone members may be selected. The bone members maycorrespond to different bones or distinct fragments of the same bone,among others. The bone members may be adjacent one another naturally ormay be moved so that they are adjacent one another. The bone members mayhave sustained or be associated with any suitable injury. For example,the bone members may result from an injury to bone (such as a fractureand/or an osteotomy, among others) or may be adjacent and/or connectedto injured soft/connective tissue (e.g., ligament, tendon, and/ormuscle, among others). In some examples, the bone members may be bonesthat articulate with one another through an anatomical joint. Anysuitable anatomical joints may be selected, including the scapholunatejoint, the acromioclavicular joint, etc. Any suitable adjacent bones maybe selected, including bones of the hand, wrist (e.g., carpal bones),arm, foot, ankle, leg, shoulder, etc.

A jointed bone connector may be selected. The jointed bone connector mayhave any combination of the features described elsewhere in the presentteachings. Furthermore, the jointed bone connector may have a size(e.g., length and width) selected according to the size of the bonemembers into which the jointed bone connector is to placed (e.g., anarrower and/or shorter jointed bone connector for smaller bone membersand a wider and/or longer jointed bone connector for larger bonemembers).

The jointed bone connector may be placed into the bone members. Inparticular, a leading anchor element of the jointed bone connector maybe advanced first through a more proximal (closer and/or moreaccessible) of the bone members and then into a more distal (fartherand/or less accessible) of the bone members. A trailing anchor elementof the jointed bone connector may follow the leading anchor element intothe proximal bone member. The anchor elements may be positioned suchthat each anchor element is at least mostly (or completely) disposedwithin a different one of the bone members. A pivotable joint of theconnector may be disposed generally between the bone members, such asoverlapping with and/or proximate to an anatomical joint through whichthe bone members articulate. The proximity of the pivotable joint to theanatomical joint may, in some cases, at least partially determine apermitted range of transverse pivotal motion of the pivotable joint,with a smaller range permitted as the pivotable joint is positionedfarther from the anatomical joint. In some examples, the jointed boneconnector may include a nonthreaded region disposed between spacedthreaded regions. Each threaded region may be placed at least mostly orcompletely in a different bone member, with the nonthreaded regionextending between the bone members. In some examples, a retentionmechanism may be actuated for one or both anchor elements to restrictremoval of the anchor element(s) from bone, after one or both anchorelements have been placed into the bone members. In some examples, oneof the anchor elements may be disposed in threaded engagement with boneduring placement into bone and the other anchor element may berestricted from removal by actuation of a retention mechanism after theother anchor element is disposed in bone.

The jointed bone connector may be placed into a pre-formed hole in thebone members. The hole may be formed, for example, by drilling throughthe proximal bone member and into the distal bone member (or viceversa). In some examples, the hole may be formed by drilling over a wireplaced into the bone members, to define a guide path along which a drilland the jointed bone connector travel. Accordingly, the drill and/orjointed bone connector may be cannulated so that each can slide alongthe wire. Alternatively, the jointed bone connector (and particularly ajointed bone screw) may be self-drilling so that it forms and/or widensits own hole as it advances into bone.

The jointed bone connector may be left in place permanently or may beremoved at a later time. Removal of the jointed bone connector may takeplace at any suitable time. Exemplary times include at a predefined timeor after a predefined amount of healing. In some examples, the jointedbone connector (and/or an anchor element thereof) may be bioresorbable,so that the jointed bone connector (and/or an anchor element thereof) isbroken down by the body over time.

VIII. KITS

The jointed bone connectors of the present teachings may be provided inkits. The kits optionally may include (1) a plurality of jointed boneconnectors, of the same and/or different sizes, (2) drills and/or othertools for forming holes for receiving jointed bone connectors, (3)drivers and/or other tools (such as gripping tools) for installingand/or removing jointed bone connectors from bone, (4) wires forreceiving and guiding jointed bone connectors, drills, and/or drivers,as appropriate, and/or (5) a case for holding and/or organizing othercomponents of the kit. Components of the kit may be sterile and/orsterilizable (e.g., autoclavable). In some examples, components of thekit, such as jointed bone connectors and/or wires, may be intended forsingle use. In some examples, components of the kit, such as drillsand/or drivers, may be intended or suitable for repeated use.

IX. EXAMPLES

The following examples describe selected aspects and embodiments ofsystems for connecting bones and/or bone fragments using a boneconnector with a pivotable joint. These examples are included forillustration and are not intended to limit or define the entire scope ofthe present teachings.

Example 1 Jointed Bone Screw 1

This example describes selected aspects of jointed bone screw 116; seeFIGS. 4-8. Additional aspects of bone screw 116 are described above inrelation to FIG. 3.

FIG. 4 shows bone screw 116 in an assembled configuration with pivotablejoint 118 directly connecting trailing screw element 120 to leadingscrew element 122. The screw elements may have any suitable size andshape. In some examples, the screw elements may have about the samediameter. Alternatively, the leading screw element may be lesser indiameter than the trailing screw element, such as having a lesseraverage diameter, a lesser maximum diameter, and/or a lesser mediandiameter than the trailing screw element. Each screw element may have abody 130, 132 on which respective external threads 124, 126 may beformed. Each body may be generally cylindrical, as shown here, and/ormay taper in a linear or nonlinear fashion, such as to create a bodythat is partially or completely frustoconical. Furthermore, a leadingregion of one or both screw elements may have a tapered nose 134, 136to, for example, facilitate centering each screw element as it entersbone.

Threads 124, 126 may have any suitable structure. For example, eachthread may have one or more tap regions 138 to facilitate forming athread in bone, generally by cutting bone. The threads may have the samepitch in each screw element or the pitches may be different. Forexample, as shown here, the leading screw element may have a greater (orlesser) pitch than the trailing screw element, which may tend to drawbone members together (or apart) as the bone screw is installed in bone.The tap regions may be disposed internally within each thread, as shownhere, may be disposed at a leading end of the thread, and/or may bespaced from the thread, such as forward of the thread on the screwelement. In some embodiments, one or more of the tap regions maystructured as a notch or flute within a thread. Further aspects ofthread structures that may be suitable are described elsewhere in thepresent teachings, such as in Section II.

FIG. 5 shows bone screw 116 with screw elements 120, 122 separated fromone another. The separated configuration shown here may represent apre-assembly configuration before the screw elements are pressedtogether to create pivotable joint 118. The screw elements may beassembled by placing a head (e.g., a ball) 140 of the leading (ortrailing) screw element into a joint cavity or socket 142 of thetrailing (or leading) screw element (see FIG. 6). After the head isreceived in the joint cavity, generally pressed into the joint cavitywith substantial force, the ball may be trapped in the joint cavity by awall 144 forming a mouth 146 of the cavity, to restrict separation ofthe screw elements (e.g., to restrict relative motion in each opposingaxial direction of the bone screw). The head may be disposed adjacent aneck 147 of the screw element. The neck may be about the same diameteras the screw element body, of greater diameter, or of lesser diameter(as shown in the present illustration).

FIGS. 6-8 shows additional cavities defined by the screw elements. Bonescrew 116 may be cannulated, that is, hollow along its length. Forexample, each screw element may include a driver engagement structure148, 150 formed as a hexagonal socket. The hexagonal sockets may be thesame size or of different size, as shown here. Sockets of different size(and/or shape) may facilitate selective and/or independent engagementand rotation of each screw element with a distinct driver (or distinctlysized driver region). Each hexagonal socket may extend any suitabledistance along its corresponding screw element, such as less than aboutone half, greater than about one half, or about the entire length. Forexample, in the present illustration, each hexagonal socket is disposedin a trailing region of its corresponding screw element and extendssubstantially less than one-half the length of the screw element. Eachscrew element also may have one or more additional cavities, each oflesser or greater diameter than the hexagonal socket. For example,trailing screw element 120 may have a cylindrical bore or other cavity152 that extends from hexagonal socket 148 to joint cavity 142.Alternatively, or in addition, leading screw element 122 may have acylindrical bore or other cavity 154 that extends from hexagonal socket150 to the leading end of the screw element. Each bore/cavity may have alarger diameter than the hexagonal socket, to allow driver advancementpast the socket, or may have a smaller diameter than the hexagonalsocket, for example, to provide a forward shoulder 156, 158 againstwhich a driver may be abutted, to restrict driver advancement and thusto position the driver axially.

Example 2 Jointed Bone Screw 2

This example describes another exemplary bone screw with a pivotablejoint; see FIGS. 9-11.

FIGS. 9-11 show respective exploded, assembled, and sectional views ofan exemplary bone screw 180 with a pivotable joint 182 that directlyconnects screw elements 184, 186. The pivotable joint of the bone screwmay be formed by a protruding portion 188, such as a widened end regionor head, of one of the screw elements received in a joint cavity 190 ofthe other screw element. The protruding portion and the joint cavity mayhave any suitable shapes that permit mating and relative pivotal motion.In the present illustration, the trailing screw element 184 has asemispherical head and the leading screw element defines a complementarysemispherical socket disposed near the trailing end of the screwelement. One or both screw elements may include a spacer or neck region192. The spacer region may be nonthreaded and configured to space thehead (or socket) from a thread 194 (or 196) (or any other suitableretention mechanism) of the trailing screw element (or leading screwelement), thereby separating external threads 194, 196 (and/or otherretention mechanisms) of screw elements 184, 186 (see FIG. 10).

FIG. 10 shows bone screw 180 in an aligned configuration. In thisaligned configuration each of screw elements 184, 186 may be disposedgenerally concentrically about a central axis 198 of the bone screw,with respective long axes of the screw elements in a collinearconfiguration.

The screw elements may have any suitable thread configuration. In thepresent illustration, trailing thread 194 and leading thread 196 haveabout the same pitch, which may be constant within each screw element.However, in other embodiments, these pitches may differ within and/orbetween the screw elements. The trailing and leading threads may definemajor diameters (e.g., measured perpendicular to the central axisbetween generally opposing crests) and/or minor diameters (e.g.,measured perpendicular to the central axis between generally opposingtroughs) that are constant or that vary within each screw element. Themajor and/or minor diameters also may be the same or different whencompared between the screw elements. In the present illustration, thetrailing screw element has substantially constant major and minordiameters along its length. In addition, the leading screw element istapered along its length toward a leading end of the screw element. Inparticular, the major diameter and the minor diameter gradually decreasetoward the leading end. Furthermore, the greatest major diameter of theleading screw element, defined by a trailing region 200 of the leadingscrew element, may be about the same as (or less than) the majordiameter of the trailing screw element, and particularly the majordiameter defined by a leading region 202 of the trailing screw element(if the major diameter varies in the trailing screw element).

Bone screw 180 also may be disposed in a bent configuration. Inparticular, the central axes of the trailing and leading screw elementsmay be moved out of alignment so that the leading screw element isdisposed at an angle to the trailing screw element. More generally, theleading screw element (and/or the trailing screw element) may movepivotably about a central axis defined by the leading screw element (orthe trailing screw element). Furthermore, the leading screw element(and/or the trailing screw element) may move pivotably about atransverse axis (or axes) defined by the pivotable joint of the bonescrew. This motion about one or more transverse axes, generally termedbending motion, may be through any angle permitted by the pivotablejoint.

FIG. 11 shows exemplary hollow structure that may be defined by bonescrew 180.

Trailing screw element may define a hollow 204 (e.g., a through-hole)extending through the screw element to each opposing end of the screwelement. The cavity may have a noncircular cross-section, such as ahexagonal geometry, at one or more (or all) positions along the trailingscrew element, to facilitate engagement by a driver (e.g., a hexagonaldriver received in a hexagonal socket). Furthermore, a trailing endregion 206 of the cavity may be beveled, to facilitate placing a driverinto the cavity.

Leading screw element 186 also may define a hollow 208 (e.g., athrough-hole) of varying cross-sectional geometry. A trailing region ofthe hollow may define a receiver structure 210 for ball structure 188.The receiver structure may include joint cavity 190 and a mouth region212 adjoining the joint cavity. The mouth region may be defined by a lip214 of the receiver structure. Accordingly, the mouth region may be partof a semispherical joint cavity, or may, for example, be a cylindricalextension of the semispherical joint cavity, as shown in the presentillustration. In any case, the mouth region generally defines a narrowedsection of the joint cavity, so that a shoulder 216 of lip 214 cancapture the ball structure in the joint cavity and thus maintaincoupling between the screw elements before, during, and afterinstallation of the bone screw. An intermediate region of hollow 208 maydefine a driver engagement structure 218, for example, a hexagonalsection of the hollow. A leading region of hollow 208 may narrowrelative to the intermediate region to define a bore 220 and form ashoulder 222. The bore may be used, for example, for placement of thebone screw over a guide wire. The shoulder may function, for example, toposition a driver axially along the bone screw and to provide a bearingsurface against which the driver may be pushed axially, to facilitateinstallation of the bone screw.

Spacer region 192 of the trailing screw element may have any suitableshape and size. In some examples, the spacer region may be generallycylindrical or frustoconical, among others. Furthermore, the spacerregion may have a smaller width (and/or diameter) than ball structure188 joined distally to the spacer region. Furthermore, the spacer regionmay be narrower than threaded region 194, for example, having a diameterless than the minor diameter of the threaded region. In some examples,the diameter of the spacer region relative to the diameter of the ballstructure may at least partially determine the maximum bending angle forthe bone screw allowed by the pivotable joint.

Example 3 Jointed Bone Screw 3

This example describes yet another exemplary bone screw 240 with apivotable joint; see FIG. 12.

Bone screw 240 may include a plurality of screw elements 242, 244coupled via a ball-and-socket joint 246. A female portion or socket 248of joint 246 may be provided by trailing screw element 242. A maleportion or ball 250 of joint 246 may be provided by leading screwelement 244.

The proximal and distal screw members, when aligned, cooperatively mayform a driver engagement structure 252 for receiving a driver. In someembodiments, the driver engagement structure may be formed by portionsforming a hole, such as a hexagonal socket, with a constant crosssection. The trailing portion of the hexagonal socket may extend axiallyat least substantially or completely from the trailing end of thetrailing screw element to joint socket 248. The leading portion of thehexagonal socket may extend any suitable distance along leading screwelement 244. In some examples, the leading portion may be restricted atleast substantially to ball 250 of the leading screw element. The ballmay have a larger diameter than the minor diameter of the leading screwelement. Accordingly, restricting the leading portion of the hexagonalsocket to the ball may permit the hexagonal socket to be wider and/orthe threaded region of the distal screw member to be narrower than inthe jointed bone screw of Example 2.

Example 4 Jointed Bone Screw with Translational Play

This example describes an exemplary bone screw 260 with a pivotablejoint that permits translational play of screw elements; see FIG. 13.

Bone screw 260 may include a pivotable joint 262 formed by a pair ofscrew elements 264, 266. Trailing screw element 264 may define an oblongsocket 268 that receives a head 270 of the leading screw element (orvice versa). Socket 268 may be substantially larger than the head in anaxial direction (oversized axially), to permit the head to slideaxially, as indicated at 272 by a double-headed arrow. Accordingly, thesocket may have a central region 274 that is relatively cylindrical.Alternatively, or in addition, the socket may be oversized transversely,to permit transverse play of the head within the socket. Any degree ofaxial and/or transverse play may be suitable, such as at least aboutone, two, or five millimeters.

Example 5 Jointed Bone Connector with Deformation Features

This example describes an exemplary jointed bone connector 290 withdeformation-based retention mechanisms that can be actuatedindependently and selectably with the connector disposed in bone; seeFIGS. 14-15.

Jointed bone connector 290 may include a trailing anchor element 292 anda leading anchor element 294 connected by a pivotable joint 296. Eachanchor element may have a cross-sectional dimension (such as a diameter)that can be increased by selective deformation of the anchor element ata suitable time, generally with the anchor element suitably disposed inbone.

The leading anchor element may be configured as a blind rivet with anonthreaded retention mechanism 298 (see FIG. 15). The leading anchorelement may include a leading body member 302 that engages bone anddefines a cavity 304 configured to receive an actuation element 306forced (e.g., pulled) into the cavity. The actuation element may be amandrel having a head 308 and a stem or extension region 310 extendingtoward the trailing end of the connector from the head. The head (suchas a ball) may be oversized relative to the cavity, such that walls 312of the cavity are deformed outward, shown at 314, as the head moves into(or within) the cavity (leftward in the present illustration). The stemof the actuation element may extend through an axial bore 316 of thetrailing anchor element and out of the trailing end of the trailinganchor element, so that the stem is accessible to a gripping tool. Inparticular, the stem may be gripped by the tool and then pulled awayfrom the connector, to force the head of the actuation element into thecavity. The cavity may narrow (and/or taper) toward the trailing anchorelement, shown at 318, to restrict further movement of the head.Accordingly, the stem of the actuation element may be configured to bedetachable (e.g., broken off) after the leading retention mechanism hasbeen actuated. (The stem of the actuator element is shown in phantomoutline here to indicate its removal after detachment.) The process ofactuation may anchor the leading anchor element in a distal bone memberby engagement of leading body member 302 with bone.

The proximal anchor element may be retained in bone by actuation of atrailing retention mechanism 320. The trailing anchor element mayinclude a trailing body member 322 that engages bone and a trailingactuation element 324 threadably coupled (or capable of being coupled)to the trailing body member (see FIG. 15). In particular, the trailingbody member may have an internal thread 326 that engages an externalthread 328 of the trailing actuation element. The trailing actuationelement (and/or the external and/or internal thread) may taper towardthe leading end of the connector so that threaded advancement of theactuation element into the trailing body member exerts a lateral(expansion) force on the trailing body member. The wall of the trailingbody member may define axial openings 330 and intervening wall segments332 (see FIG. 14). The wall segments may be bent outward as theactuation element is advanced rotationally (for example, with a driverdisposed in recess 332 (see FIG. 15), to engage bone and thus retain thetrailing anchor element in a proximal bone member.

Example 6 Exemplary Drivers

This example describes exemplary drivers that may be suitable forinstallation of jointed bone connectors; see FIGS. 16-18.

FIGS. 16 and 17 show an exemplary driver 360 suitable for rotationallydriving jointed bone screws into bone. Driver 360 may include a shaft362 coupled fixedly or removably to a handle 364. The shaft may includean extension region 366 joined to a hexagonal tip region 368. The handlemay be configured to be gripped by hand and may be substantially greaterin diameter than the shaft, to generate more torque when turned by hand.

The hexagonal tip region may be configured to be complementary to,received in, and to engage a hexagonal socket in a jointed bone screw,such as the socket described in Example 2 (see FIG. 11) and Example 3(see FIG. 12). Accordingly, the tip region may be sized according to thediameter and length of the hexagonal socket. In some embodiments, thetip region may be shorter than the socket. For example, a shoulder 370formed at the distal end of extension region 366 may bear against theproximal end of the jointed bone screw when the hexagonal tip region isfully received in the hexagonal socket of the bone screw, to promoteexerting an axial force on the bone screw. Alternatively, the tip regionmay be longer than the hexagonal socket, such that the distal end of thetip region bears against a shoulder formed in the bone screw (such asshoulder 222 of FIG. 11).

FIG. 18 shows another exemplary driver 380 for jointed bone connectors.Driver 380 may include a hexagonal tip region 382 with a steppedconfiguration to create hexagonal engagement regions 384, 386 ofdifferent cross-sectional sizes (i.e., different diameters). Inparticular, proximal engagement region 384 may be configured to bereceived in and to engage a hexagonal socket of larger diameter anddistal engagement region 386 may be configured to be received in and toengage a hexagonal socket of smaller diameter. An exemplary jointed bonescrew that may be suitable for use with driver 380 is described inExample 1 (see FIG. 6).

Drivers may be used in any suitable manner to engage and turn screwelements of a jointed bone screw. For example, both the leading andtrailing screw elements of a screw may be engaged and turned at the sametime, to thread the screw elements as a unit into bone. Alternatively,either a leading or a trailing screw element may be engaged and turnedselectively with a suitable driver, to selectively move only one of thescrew elements in relation to its engaged bone member. Accordingly,selective forward or reverse movement of only one of the screw elementsmay allow adjustment of the spacing between engaged bone members. Forexample, selective forward advancement (or reverse movement) of theleading screw element may decrease (or increase) the spacing betweenbone members. Furthermore, selective forward advancement (or reversemovement) of the trailing screw element may increase (or decrease) thespacing between bone members. Selectively driving only one of the screwelements of a bone screw may be performed by driver placement (e.g., byadvancing the driver partially into only the more proximal region of ahexagonal socket for selective engagement only with the trailing screwelement). Alternatively, or in addition, selective driving may beperformed by the choice of driver structure, for example, by selecting adriver with a shorter tip region (so that the driver does not extend tothe leading screw element) and/or by selecting a driver with a tipregion of smaller diameter (so that the tip region cannot engage a widersocket in the trailing screw element).

Example 7 Bone Screw with Cylindrical Joint

FIG. 19 shows a schematic representation of an exemplary bone screw 400.The screw includes a leading screw element 402 and a trailing screwelement 404 connected by a pivotable joint 406. The joint is formed by acylindrical protuberance 408 of leading screw element 402 trapped in acylindrical cavity 410 of trailing screw element 404.

Example 8 Selected Embodiments

This example describes selected aspects and embodiments of the presentteachings, presented as a series of indexed paragraphs.

1. A device for connection of at least two bone members, comprising: (A)a proximal anchor element configured to be anchored in a proximal bonemember; and (B) a distal anchor element configured to be anchored in adistal bone member, wherein the proximal and distal anchor elementsdefine a cavity and a projection received in the cavity to form apivotable joint that connects the proximal and distal anchor elementsand allows relative bending motion of the anchor elements.

2. The device of paragraph 1, wherein each of the proximal and distalanchor elements includes an external thread for engagement with bone.

3. The device of paragraph 1, wherein at least one of the proximal anddistal anchor elements includes a retention mechanism that can beactuated to anchor the at least one anchor element in a bone at aselectable time after the at least anchor element is disposed in bone.

4. The device of paragraph 3, wherein actuation of the retentionmechanism deforms the at least one anchor element.

5. The device of paragraph 4, wherein the at least one anchor elementincludes a body member that engages bone and an actuation element thatis movable within the body member to deform the body member.

6. The device of paragraph 5, wherein the actuation element includes anexternal thread, and wherein the retention mechanism can be actuated byturning the actuation element.

7. The device of paragraph 5, wherein the actuation element includes anextension region that extends proximally from the at least one anchorelement, and wherein the extension region is configured to be pulledproximally to deform the at least one anchor element.

8. The device of paragraph 7, wherein at least a portion of theextension region is configured to break off from the actuation elementafter the at least one anchor element has been deformed by pulling theactuation element.

9. The device of paragraph 3, wherein the at least one proximal anddistal anchor element includes each of the proximal and distal anchorelements.

10. The device of paragraph 3, wherein only one of the proximal anddistal anchor elements includes the retention mechanism, and wherein theother of the proximal and distal anchor elements includes an externalthread configured to engage bone.

11. The device of paragraph 1, wherein at least one of the proximal anddistal anchor elements is configured to engage bone sufficiently foranchorage during placement into the bone.

12. The device of paragraph 11, wherein the at least one anchor elementis configured to be anchored in bone by driving the at least one anchorelement translationally into the bone.

13. The device of paragraph 11, wherein the at least one anchor elementis configured to be anchored in bone by driving the at least one anchorelement rotationally into the bone.

14. A bone screw for connection of at least two bone members comprising:(A) a proximal anchor element having an external thread for engaging aproximal bone member; and (B) a distal anchor element having an externalthread for engaging a distal bone member, wherein the proximal anddistal anchor elements define a cavity and a projection received in thecavity to form a pivotable joint that connects the proximal and distalanchor elements and allows relative bending motion of the anchorelements.

15. The bone screw of paragraph 14, wherein the proximal and distalanchor elements cooperatively define a bore having a noncircular crosssection and configured to receive a driver that turns the anchorelements for installation in bone.

16. The bone screw of paragraph 15, wherein the distal anchor elementincludes a proximal section and a distal section, and wherein the boreat least one of narrows and terminates within the distal section.

17. The bone screw of paragraph 14, wherein the proximal anchor elementdefines a long axis, and wherein the pivotable joint permits relativepivotal motion of the proximal and distal anchor elements about the longaxis.

18. The bone screw of paragraph 17, wherein the pivotal motion about thelong axis is unrestricted such that the distal anchor element can berotated through a full turn.

19. The bone screw of paragraph 14, wherein the projection is defined bythe proximal anchor element, and wherein the projection is generallyspherical.

20. The bone screw of paragraph 14, wherein each of the proximal anddistal anchor elements includes a thread having a pitch, and wherein thepitch is about the same for the anchor elements.

21. The bone screw of paragraph 14, wherein the distal anchor elementincludes a length, a distal end, and a thread defining a major diameter,and wherein the major diameter of the thread decreases gradually towardthe distal end along a substantial portion of the length.

22. The bone screw of paragraph 21, wherein the major diameter of thedistal anchor element has a maximum, wherein the proximal anchor elementincludes a thread defining a major diameter with an average, and whereinthe maximum is about the same as the average.

23. The bone screw of paragraph 14, wherein each of the proximal anddistal anchor elements is unitary.

24. The bone screw of paragraph 14, wherein each of the proximal anddistal anchor elements includes a threaded region, and wherein at leastone of the proximal and distal anchor elements includes a nonthreadedregion disposed generally between the threaded regions.

25. The bone screw of paragraph 24, wherein the nonthreaded region isincluded in the one anchor element having the projection, and whereinthe nonthreaded region is disposed generally between the projection andthe threaded region of the one anchor element.

26. A kit for connection of at least two bone members, comprising: (A) afirst device or bone screw according to any one of paragraphs 1-25; and(B) at least one of a second device or bone screw according to any oneof paragraphs 1-25, a drill for forming a hole in bone for receiving thefirst device or bone screw, a driver for installing and/or removing thefirst device or bone screw from bone, and a wire for receiving a bonescrew, driver, and/or drill.

27. A method of connecting bone members, comprising: (A) selecting apair of adjacent bone members; (B) selecting a device or bone screwaccording to any one of paragraphs 1-25; and (C) installing the deviceor bone screw in the adjacent bone members such that each anchor elementis at least substantially disposed in a different bone member.

28. The method of paragraph 27, wherein the step of selecting a pair ofadjacent bone members includes selecting a scaphoid bone and a lunatebone.

The disclosure set forth above may encompass multiple distinctinventions with independent utility. Although each of these inventionshas been disclosed in its preferred form(s), the specific embodimentsthereof as disclosed and illustrated herein are not to be considered ina limiting sense, because numerous variations are possible. The subjectmatter of the inventions includes all novel and nonobvious combinationsand subcombinations of the various elements, features, functions, and/orproperties disclosed herein. The following claims particularly point outcertain combinations and subcombinations regarded as novel andnonobvious. Inventions embodied in other combinations andsubcombinations of features, functions, elements, and/or properties maybe claimed in applications claiming priority from this or a relatedapplication. Such claims, whether directed to a different invention orto the same invention, and whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the inventions of the present disclosure.

We claim:
 1. A bone screw, comprising: a first screw element and a second screw element each including an external thread for threaded engagement with bone, the screw elements being connected by a pivotable joint that traps a cylindrical protuberance of the first screw element in a cylindrical cavity of the second screw element to block removal of the cylindrical protuberance from the cylindrical cavity, wherein the cylindrical protuberance and the cylindrical cavity are formed by a leading end region of one of the screw elements and a trailing end region of the other screw element, and wherein the cylindrical protuberance is movable in the cylindrical cavity to permit (a) the screw elements to be turned relative to one another about a longitudinal axis defined by a screw element and (b) the bone screw to be bent about a transverse axis of the bone screw from a coaxial arrangement of the screw elements.
 2. The bone screw of claim 1, wherein the cylindrical cavity includes a tapered region that blocks removal of the cylindrical protuberance from the cylindrical cavity.
 3. The bone screw of claim 1, wherein the cylindrical cavity includes a mouth that is narrower than a diameter of the cylindrical protuberance such that withdrawal of the protuberance from the cylindrical cavity is resisted.
 4. The bone screw of claim 1, wherein the pivotable joint permits the bone screw to be bent to an angle of at least about 5 degrees from a coaxial arrangement of the screw elements.
 5. The bone screw of claim 4, wherein the pivotable joint permits the bone screw to be bent to an angle of about 5 to 20 degrees.
 6. The bone screw of claim 1, wherein the screw elements are a leading screw element and a trailing screw element, wherein the trailing screw element defines a central channel extending longitudinally through the trailing screw element, and wherein the leading screw element includes a driver engagement structure that is accessible to mate with a corresponding driver advanced to the driver engagement structure via the central channel.
 7. The bone screw of claim 6, wherein the cylindrical protuberance is provided by the trailing screw element and forms a portion of the central channel.
 8. The bone screw of claim 6, wherein the cylindrical protuberance is formed by the leading screw element and defines an opening that communicates with the central channel.
 9. The bone screw of claim 6, wherein the external thread of the leading screw element has a larger pitch than the external thread of the trailing screw element, thereby providing compression when the screw elements are driven into bone.
 10. The bone screw of claim 6, wherein the leading screw element is smaller in diameter on average than the trailing screw element.
 11. The bone screw of claim 1, wherein each of the screw elements is only one discrete piece.
 12. The bone screw of claim 1, wherein the screw elements are movable relative to one another via axial motion of the cylindrical protuberance in the cylindrical cavity.
 13. A method of connecting bones with a pair of screw elements connected by a pivotable joint that traps a cylindrical protuberance of one of the screw elements in a cylindrical cavity of the other screw element to block removal of the cylindrical protuberance from the cylindrical cavity, with the cylindrical protuberance and the cylindrical cavity being formed by a leading end region of a first of the screw elements and a trailing end region of a second of the screw elements, the cylindrical protuberance being movable in the cylindrical cavity to permit (a) the screw elements to be turned relative to one another about a longitudinal axis defined by a screw element and (b) the bone screw to be bent about a transverse axis of the bone screw from a coaxial arrangement of the screw elements, the method comprising: driving the bone screw into a pair of bones such that an external thread of each screw element is disposed in threaded engagement with a different bone.
 14. The method of claim 13, wherein the pair of bones are leg bones.
 15. The method of claim 13, wherein the cylindrical cavity includes a tapered region that blocks removal of the cylindrical protuberance from the cylindrical cavity.
 16. The method of claim 13, wherein the pivotable joint permits the bone screw to be bent to an angle of at least about 5 degrees.
 17. The method of claim 13, wherein the screw elements are a leading screw element and a trailing screw element, wherein the trailing screw element defines a central channel extending longitudinally through the trailing screw element, and wherein the leading screw element includes a driver engagement structure that is accessible to mate with a corresponding driver advanced to the driver engagement structure via the central channel.
 18. The method of claim 17, wherein the cylindrical protuberance is provided by the trailing screw element and forms a portion of the central channel.
 19. The method of claim 17, wherein the cylindrical protuberance is formed by the leading screw element and defines an opening that communicates with the central channel.
 20. The method of claim 17, wherein the external thread of the leading screw element has a larger pitch than the external thread of the trailing screw element, thereby providing compression when the bone screw is driven into the pair of bones. 